/Engine/Plugins/Runtime/GeometryProcessing/Source/DynamicMesh/Public/Parameterization/MeshRegionGraph.h
Incrementally merge regions with a triangle count below the given SmallThreshold. A Small region is merged to it's most-similar neighbour, as defined by RegionSimilarityFunc. The merge order is sorted by largest Similarity, ie most-similar regions are merged first.
bool MergeSmallRegions ( int32 SmallThreshold, [TFunctionRef](API\Runtime\Core\GenericPlatform\TFunctionRef)< float(int32 SmallRgnIdx, int32 NbrRgnIdx)> RegionSimilarityFunc )